The most common and most likely answer to this crossword clue is the 11 letter word INTRAVENOUS
I've seen this crossword clue in The Times
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More clues leading to the result INTRAVENOUS
Buddy explains!

The straight part
We know that "Type of injection" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case type of injection = intravenous.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INTRAVENOUS mean?
INTRAVENOUS noun- A dose of medicine administered from a drip, down through a hollow needle inserted into a patient's vein.
- Inside the veins.